Many communication systems used today employ I-Q modulation and demodulation schemes to transmit and receive information at increased rates. In these schemes, the output of a transmitter, as well as the input of a receiver, includes both an in-phase and quadrature-phase signal. Ideally, the quadrature-phase signal is 90 degrees out of phase with the in-phase signal. Unfortunately, modern wireless systems mandate high levels of circuit integration and stringent power consumption requirements. These demands lead to various imperfections in radio-frequency (“RF”) front end circuits. Thus, in many of these systems, a mismatch or imbalance exists between the quadrature-phase and in-phase signals, such that the phase difference is not 90 degrees. The I-Q mismatch corrupts the spectral purity of the received signal thereby resulting in higher bit error rates (“BER”) in the communication systems. This impairment is of great significance in increasingly popular wideband communication systems.
Significant research has been devoted to measuring and compensating for I-Q mismatch in wireless communication systems. Unfortunately, this research has failed to produce a simple and efficient method of addressing I-Q mismatch. For example, some conventional methods provide adaptive methodology of correcting I-Q mismatch in quadrature modulators/demodulators using an envelope detector to down-convert the RF signal. These methods try to minimize the least squares error in obtaining the coefficients of the compensator block. The proposed methodology of these conventional systems is computationally intensive and does not necessitate the estimation of the imperfection specification. Another conventional method uses a loopback method to estimate the parametric variations in I-Q mismatch and time skew, which requires a time intensive iterative method. Yet another conventional method uses spectral analysis for I-Q mismatch cancellation and LO leakage suppression, which requires significant time and hardware overhead. Still yet another conventional method exploits the presence of an extra loopback receiver (placed for performing digital pre-distortion of HPA) to cored for I-Q mismatch and DC offset errors. The received constellations along with programmable digital-to-analog converter (“DAC”) components are utilized to make corrections. These methods require full demodulators and spectrum analyzers, which make the procedures costly.
Therefore, a desire exists for simple and cost efficient systems and methods for measuring and compensating for the I-Q mismatch in communication systems. Embodiments of the present invention provide such systems and methods.